1. Field of the Invention
The present invention relates to a valve for the treatment of hydrocephalus.
It is known that hydrocephalus is a pathological state resulting in an abnormal increase of cerebrospinal fluid (CSF) into the ventricles of the brain. Most of the time hydrocephalus arises from an obstruction in the sites of absorption of the CSF, usually referred to as arachnoid villi which are the natural pathways of the CSF into the venous blood. Such obstruction, if not treated, results in an enlarged head in infants whose cranial sutures have not yet fused, with subsequent brain damage. In adults, because of the rigidity of the skull, the brain is subjected to an increased stress under the CSF pressure, and symptoms of headache, gait disturbance and dementia are reported.
The treatment of choice of hydrocephalus consists in diverting the cerebrospinal fluid contained in the ventricles of the cranial cavity towards any other absorptive area such as the heart or the peritoneum.
Usual procedures consist in introducing a catheter into the ventricles through a burr hole made into the skull, this catheter being connected to a shunt pressure valve inserted under the scalp, said valve being connected to another catheter leading subcutaneously either to the heart or to the peritoneum.
Therefore the assembly comprises an upstream catheter and a downstream catheter, but in fact it constitutes a unitary system which must be connected once or twice, according to the particular model utilized. The shunt assembly from its proximal end to its distal end is completely subcutaneous, thus affording a certain freedom of movement to the patient and avoiding infections.
Consequently, when a system for diverting the cerebro-spinal fluid is implanted in a patient, an adequate valve system must be inserted therein.
The valve is placed either at the end of the systems and is therefore referred to as a distal valve, or is placed near the burr hole and in this case is referred to as a proximal valve.
2. The Prior Art
A number of valve types have already been proposed up to now for such shunting systems used in the treatment of hydrocephalus.
The applicant's prior U.S. Pat. No. 4 443 214 discloses a valve adapted to be inserted between a ventricular catheter and a draining catheter comprising a body of flattened cylindrical shape enclosing a chamber having formed through its cylindrical wall an inlet passage for introducing the cephalorachidian fluid and an outlet passage for discharging this fluid. At the inner end of the inlet passage is a frustoconical seat engageable by a ball valve acting as a non-return valve. This ball valve is urged against the seat by a curved spring blade extending along the lateral inner wall of the chamber and mounted preferably in overhanging relationship on a diameter bar of magnetic material mounted in turn for concentric rotation on a pivot pin extending across the chamber. A tooth carried by the bar end opposite the spring blade is adapted to engage detent-positioning dents formed in the lateral wall of the chamber.
The advantage of such a valve is to give to a neurosurgeon the possibility of adapting externally and thus non invasively, the pressure of the valve to the condition of a patient according to the evaluation of the size of the ventricles and/or the measurement of the intracranial pressure.
However there is a category of patients who have already been implanted with a valve and who are reported to have a "siphon effect" consisting in a sharp negativation of their intracranial pressure everytime they stand up. Most of the time the valve that has been implanted originally was either of a low pressure gradient, and/or of a low resistance type. In such case the diversion of the CSF is made exclusively through the valve and the patient has become "shunt dependant". It may be also considered that some patients have no more distal resistance at the outlet of their catheter (peritoneal) and then, there is no damper effect when standing up, the so-called "siphon effect" becoming immediate and maximal in such cases.
When symptoms of severe syphon effect are reported to neurosurgeon, a revision of the implanted valve by a valve of a higher gradient is performed. However the closing pressure remains high even in the horizontal position, and there is no adjustment of the counter pressure of the valve according to the various positions of the patient's body.